Changing IOR for Subsurface Scattering in Cycles
Well, I'm really happy that you asked this question.  I decide to try using the Fresnel Input Node to modulate the various Input sockets of the SSS shader and the results are interesting.  Using Fresnel for the radius adds depth, but it does dampen the SSS effect for the front facing poly's, so maybe it would be better to mix this setup with a stock SSS node.  Using 3 Fresnel Nodes with different IOR values and a Combine node for the Radius not only adds depth but adds a tone gradient which makes the SSS results interesting I think.  

Here is a basic setup which uses a model that I recently rebuilt for someone so it can be used with Cycles bake.  

There is an Environment Texture set to a value of 3 and a front facing overhead sun light at about 11:00. 

The model on the Left uses a stock SSS shader with radius values of 0.9, 1.5, 0.7. for the hair.  The values are 2.0, 1.45, 0.35 for the face.

The model in the center uses a Fresnel node plugged directly into the Radius of an SSS node so all 3 values have the same input.

The model on the right uses 3 separate Fresnel nodes to control the 3 values of Radius for the SSS node.  The Fresnel values are the same as the radius values for the model on the left.

It's subtle and mostly just visible at the edges the way I did it here, but if you put some effort into it you may get somewhere with this.